HP OpenVMS Systems Documentation

Examples of Copy and Merge Operations

Example 6-1 shows what happens when you create a shadow set by mounting two
disk volumes that have never been a part of a shadow set. Because
neither disk volume has been a part of a shadow set, the Mount utility
(MOUNT) assumes that the first disk named in the MOUNT command is
the source member. When the Mount utility checks the volume labels
on the disks, it discovers that they are different from each other,
and the utility automatically performs a copy operation.

In this example, DSA0 is the virtual unit name,
$1$DUA8 and $1$DUA89 are the names of the disk volumes, and SHADOWDISK
is the volume label.

The SHOW DEVICE display in Example 6-1 shows the shadow set
during the copy operation (transient state). Because the SCB information
on $1$DUA8 and $1$DUA89 indicates that these devices have never been
part of a shadow set, the shadowing software uses the first device
named in the command line ($1$DUA8) as the source of the copy operation.
The device status “ShadowSetMember” indicates that the
$1$DUA8 device is a source shadow set member, and “ShadowCopying”
indicates that the physical device $11$DUA89 is the target of a copy
operation.

Suppose you want to add a new member to an existing
shadow set, and the device you add is a previous member of this same
shadow set. In this case, the volume label of the new member matches
that of the current shadow set members, but the new member's
MOUNT generation number is out of date compared with those of the
current members. Thus, the Mount utility automatically performs a
copy operation on that member.

Example 6-2 shows the format of the MOUNT command and MOUNT status messages
returned when you add the $3$DIA12 device to the shadow set represented
by the DSA9999 virtual unit. Notice that you do not need to list the
member units currently in the shadow set on the MOUNT command line.

Example 6-3 shows what happens when a three-member shadow set is dissolved
on one node and then is immediately remounted on another node. When
the Mount utility checks the volume information on each member, it
finds that the volume information is consistent across the shadow
set. Thus, a copy operation is not necessary when the shadow set is
mounted.

In Example 6-3, DSA10 is the virtual unit and $3$DUA10, $3$DUA11, and $3$DUA12
are the member volumes. The first part of the example displays the
output from a SHOW DEVICE command, which shows that the shadow set
is mounted and in a steady state. Then the user dismounts the DSA10
shadow set and immediately remounts it.

Example 6-4 shows
the output from the SHOW DEVICE command at the time of the merge operation.

When a system fails, the volume information is
left in a state that shows that each shadow set member was not properly
dismounted. If you issue the MOUNT command again after the node reboots,
the shadowing software automatically performs a merge operation on
the shadow set.